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24-462: Demosponges (Demospongiae) are the most diverse class in the phylum Porifera . They include greater than 90% of all species of sponges with nearly 8,800 species worldwide (World Porifera Database). They are sponges with a soft body that covers a hard, often massive skeleton made of calcium carbonate , either aragonite or calcite . They are predominantly leuconoid in structure. Their " skeletons " are made of spicules consisting of fibers of

48-495: A top-level genus (genus summum) – was first introduced by French botanist Joseph Pitton de Tournefort in the classification of plants that appeared in his Eléments de botanique of 1694. Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine a distinct grade of organization—i.e. a 'level of complexity', measured in terms of how differentiated their organ systems are into distinct regions or sub-organs—with

72-992: A closely related ( taxonomic ) group of sponges and are considered to be a polyphyletic grouping and contained within the Demospongiae. Like bats and birds that independently developed the ability to fly, different sponges developed the ability to build a calcareous skeleton independently and at different times in Earth's history . Fossil sclerosponges are already known from the Cambrian period. Chaetetids, more formally called "chaetetid hyper-calcified demosponges" (West, 2011), are common calcareous fossils composed of fused tubules. They were previously classified as extinct corals , bryozoans , algae , stromatoporoids and sclerosponges . The chaetetid skeleton has now been shown to be of polyphyletic origin and with little systematic value. Extant chaetetids are also described. This skeleton

96-434: A distinct type of construction, which is to say a particular layout of organ systems. This said, the composition of each class is ultimately determined by the subjective judgment of taxonomists . In the first edition of his Systema Naturae (1735), Carl Linnaeus divided all three of his kingdoms of nature ( minerals , plants , and animals ) into classes. Only in the animal kingdom are Linnaeus's classes similar to

120-413: Is now known from three demosponge orders (Hadromerida, Poecilosclerida, and Agelasida). Fossil chaetetid hyper-calcified demosponges can only be classified with information on their spicule forms and the original mineralogy of their skeletons (West, 2011). Spermatocytes develop from the transformation of choanocytes and oocytes arise from archeocytes . Repeated cleavage of the zygote egg takes place in

144-604: The Homoscleromorpha do not belong in this class. The Homoscleromorpha was therefore officially taken out of the Demospongiae in 2012, and became the fourth class of phylum Porifera. Morrow & Cárdenas (2015) propose a revision of the Demospongiae higher taxa classification, essentially based on molecular data of the last ten years. Some demosponge subclasses and orders are actually polyphyletic or should be included in other orders, so that Morrow and Cárdenas (2015) officially propose to abandon certain names: these are

168-489: The Late Carboniferous , the order Spongillida split from the marine sponges, and is the only sponges to live in freshwater environments. Some species are brightly colored, with great variety in body shape; the largest species are over 1 m (3.3 ft) across. They reproduce both sexually and asexually . They are the only extant organisms that methylate sterols at the 26-position, a fact used to identify

192-623: The Precambrian deposits at the end of the Cryogenian "Snowball Earth" period. Their presence has been indirectly detected by fossilized steroids, called steranes , hydrocarbon markers characteristic of the cell membranes of the sponges, rather than from direct fossils of the sponges themselves. They represent a continuous chemical fossil record of demosponges through the end of the Neoproterozoic . The earliest Demospongiae fossil

216-451: The mesohyl and forms a parenchymella larva with a mass of larger internal cells surrounded by small, externally flagellated cells. The resulting swimming larva enters a canal of the central cavity and is expelled with the exhalant current. Methods of asexual reproduction include both budding and the formation of gemmules . In budding, aggregates of cells differentiate into small sponges that are released superficially or expelled through

240-773: The Ceractinomorpha, Tetractinomorpha , Halisarcida , Verticillitida , Lithistida , Halichondrida and Hadromerida . Instead, they recommend the use of three subclasses: Verongimorpha , Keratosa and Heteroscleromorpha . They retain seven ( Agelasida , Chondrosiida , Dendroceratida , Dictyoceratida , Haplosclerida , Poecilosclerida , Verongiida ) of the 13 orders from Systema Porifera. They recommend to resurrect or upgrade six order names ( Axinellida , Merliida , Spongillida , Sphaerocladina , Suberitida , Tetractinellida ). Finally, they create seven new orders ( Bubarida , Desmacellida , Polymastiida , Scopalinida , Clionaida , Tethyida , Trachycladida ). These added to

264-462: The basic toolkit of meiosis and recombination were present early in eukaryote evolution. The most economically important group of demospongians to human are the bath sponges . These are harvested by divers and can also be grown commercially. They are bleached and marketed; the spongin gives the sponge its softness. Class (biology) The class as a distinct rank of biological classification having its own distinctive name – and not just called

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288-450: The classes used today; his classes and orders of plants were never intended to represent natural groups, but rather to provide a convenient "artificial key" according to his Systema Sexuale , largely based on the arrangement of flowers. In botany, classes are now rarely discussed. Since the first publication of the APG system in 1998, which proposed a taxonomy of the flowering plants up to

312-489: The early nineteenth century. Homoscleromorpha Homosclerophorida is an order of marine sponges . It is the only order in the monotypic class Homoscleromorpha . The order is composed of two families: Plakinidae and Oscarellidae . Homoscleromorpha is phylogenetically well separated from Demospongiae . Therefore, it has been recognized as the fourth class of sponges. It has been suggested that Homoscleromorpha are more closely related to eumetazoans than to

336-581: The genera Oscarella and Pseudocorticium . These sponges are massive or encrusting in form and have a very simple structure with very little variation in spicule form (all spicules tend to be very small). Reproduction is viviparous and the larva is an oval form known as an amphiblastula . This form is usual in calcareous sponges but is less common in other sponges. Homoscleromorpha are exclusively marine sponges that tend to encrust on other surfaces at shallow depths. These sponges typically inhabit shady locations, under overhangs and inside caves. In

360-427: The largest revision of this group (from genera, subfamilies, families, suborders, orders and class) since the start of spongiology in the mid-19th century. In this large revision, the extant Demospongiae were organized into 14 orders that encompassed 88 families and 500 genera. Hooper and van Soest (2002) gave the following classification of demosponges into orders: However, molecular and morphological evidence show that

384-503: The level of orders, many sources have preferred to treat ranks higher than orders as informal clades . Where formal ranks have been assigned, the ranks have been reduced to a very much lower level, e.g. class Equisitopsida for the land plants, with the major divisions within the class assigned to subclasses and superorders. The class was considered the highest level of the taxonomic hierarchy until George Cuvier 's embranchements , first called Phyla by Ernst Haeckel , were introduced in

408-427: The oscula. Gemmules are found in the freshwater family Spongillidae . They are produced in the mesohyl as clumps of archeocytes, are surrounded with a hard layer secreted by other amoebocytes. Gemmules are released when the parent body breaks down, and are capable of surviving harsh conditions. In a favorable situation, an opening called the micropyle appears and releases amoebocytes, which differentiate into cells of all

432-664: The other sponge groups, rendering sponges paraphyletic. This view has not been supported by later work using larger datasets and new techniques for phylogenetic inference, which tend to support sponges as monophyletic, with Homoscleromorpha grouping together with Calcarea . On the basis of molecular and morphological evidence, the two families Plakinidae and Oscarellidae have been reinstated. There are 117 species in this group divided into 9 genera. The spiculate genera in this group are Aspiculophora , Corticium , Placinolopha , Plakina , Plakinasterella , Plakortis and Tetralophophora . The aspiculate species are

456-437: The other types. The cytological progression of porifera oogenesis and spermatogenesis ( gametogenesis ) shows great similarity to other metazoa. Most of the genes from the classic set of meiotic genes conserved in eukaryotes are upregulated in the sponges Geodia hentscheli and Geodia phlegraei including genes for DNA recombination . Since porifera are the earliest divergent animals, these findings indicate that

480-661: The presence of demosponges before their first known unambiguous fossils. Because of many species' long life span (500–1,000 years) it is thought that analysis of the aragonite skeletons of these sponges could extend data regarding ocean temperature , salinity , and other variables farther into the past than has been previously possible. Their dense skeletons are deposited in an organized chronological manner, in concentric layers or bands. The layered skeletons look similar to reef corals . Therefore, demosponges are also called coralline sponges . The Demospongiae have an ancient history. The first demosponges may have appeared during

504-467: The protein spongin , the mineral silica , or both. Where spicules of silica are present, they have a different shape from those in the otherwise similar glass sponges . Some species, in particular from the Antarctic, obtain the silica for spicule building from the ingestion of siliceous diatoms . The many diverse orders in this class include all of the large sponges. About 311 million years ago, in

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528-613: The recently created orders ( Biemnida and Chondrillida ) make a total of 22 orders in the revised classification. These changes are now implemented in the World Porifera Database part of the World Register of Marine Species. Sclerosponges were first proposed as a class of sponges, Sclerospongiae , in 1970 by Hartman and Goreau. However, it was later found by Vacelet that sclerosponges occur in different classes of Porifera . That means that sclerosponges are not

552-658: The start of the Tommotian stage about 530 Ma, found in southeast Siberia. A major radiation occurred in the Lower Cambrian and further major radiations in the Ordovician possibly from the middle Cambrian. The Systema Porifera (2002) book (2 volumes) was the result of a collaboration of 45 researchers from 17 countries led by editors J. N. A. Hooper and R. W. M. van Soest. This milestone publication provided an updated comprehensive overview of sponge systematics ,

576-587: Was discovered in the lower Cambrian (Series 2, Stage 3; approximately 515 Ma) of the Sirius Passet Biota of North Greenland: this single specimen had a spicule assemblage similar to that found in the subclass Heteroscleromorpha . The earliest sponge-bearing reefs date to the Early Cambrian (they are the earliest known reef structure built by animals), exemplified by a small bioherm constructed by archaeocyathids and calcified microbes at

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